Another evidence for effective thinning of the sample S is found in the enhanced coercivity revealed in the \(m-H\)  hysteresis curves. As plotted in Fig. REF (d), the sample S has significantly larger coercive field (\(H^S_c \approx \)  1.3 kOe) than the sample L at 0.30 kOe although the former has smaller moment in zero field. This behavior is consistent not only with the previous independent observations of the bulk and monolayer samples [1]}, [2]}, but also the recent report of surface layers being harder than the bulk by the magnetic force microscopy measurements [3]}. Therefore, we conclude that the sample S is closer to the monolayer limits than the sample L.
